Haha are you seriously asking if an anti-virus is worth it? Of course it is! You really have to have one nowadays, you can get a virus anywhere.
And if you're wondering, look at
http://www.matousec.com/projects/firewall-challenge/results.php#firewalls-ratings.
They have all of the best firewall ratings. Whats even better, is one of the best rated firewalls and antivirus is Comodo, which is completely free.